1. Technical Field
One or more embodiments of the present invention relate to a three-dimensional shape measuring apparatus, a three-dimensional shape measuring method, and a three-dimensional shape measuring program for analyzing an optical pattern, which is projected to a measurement target, to measure a three-dimensional shape of the measurement target.
2. Background Art
As means for obtaining three-dimensional shape information on a target object through an image analysis, there is a method for projecting an optical pattern to a measurement target existing in a predetermined imaging visual field to analyze a deformation amount of the optical pattern changed according to a three-dimensional shape of the measurement target. A light cutting method, a spatial code method, and a fringe analysis method can be cited as typical methods. These methods are based on a principle of a triangulation. Among others, various techniques such as a spatial fringe analysis and a temporal fringe analysis are proposed with respect to the fringe analysis method, and the fringe analysis method is known as a technique of obtaining high measurement accuracy (Patent Documents 1 to 3 and Non-Patent Document 1).
In the case of the above method, a geometrical positional relationship among a phototransmitting device that projects the optical pattern, a reference plane that is a plane on which the measurement target is placed, and an imaging device that captures an image of the measurement target affects the measurement accuracy in a height position. This point will be described with reference to FIG. 15.
FIG. 15 is a view illustrating the principle of the triangulation. For the convenience of explanation, a plane Ph having a height h from a reference plane P0 is observed with an imaging device Cc having an optical axis perpendicular to the reference plane P0. A phototransmitting device Cp is disposed at the same level as the imaging device Cc when viewed from the reference plane P0, and the optical pattern is projected to a position of a point O on the reference plane P0.
In the case where the plane Ph that is parallel with the reference plane P0 and separated by the height h is observed, the optical pattern directed to the point O intersects a point P. At this point, when the plane Ph is viewed from the imaging device Cc, the optical pattern projected to the point P0 is observed in a position P having a distance PQ from an optical axis (Z-axis). This position deviation PQ emerges as a phase difference of the optical pattern. When the phase difference can be computed, the height h can be computed by the following equation (1).
                    [                  Formula          ⁢                                          ⁢          1                ]                                                            h        =                              L            d                    ·                      PQ            _                                              (        1        )            
(Where PQ expresses a distance between PQ, namely, a phase difference. In addition, d expresses a distance between centers of optical axes of an imaging portion Cc and a phototransmitting portion Cp, and L expresses a distance from the imaging portion Cc to a reference plane, and the distance d and the distance L are well-known values.)    Patent Document 1: Japanese Unexamined Patent Publication No. 2002-286433 (published on Oct. 3, 2002)    Patent Document 2: Japanese Unexamined Patent Publication No. 2004-117186 (published on Apr. 15, 2004)    Patent Document 3: Japanese Unexamined Patent Publication No. 2007-114071 (published on May 10, 2007)    Patent Document 4: Japanese Unexamined Patent Publication No. 2002-214147 (published on Jul. 31, 2002)    Patent Document 5: Japanese Unexamined Patent Publication No. 2005-300512 (published on Oct. 27, 2005)    Non-Patent Document 1: Fujigaki, et al., “Grating Projecting Method on Shape Measurement for Continuous Object by Multiple Linear Sensors”, Proceedings of JSPE Autumn Meeting, the Japan Society for Precision Engineering, pp. 1061-1062, 2004